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Fire safety greatly contributes to feeling safe, and it is a key parameter for the selection of building materials. The combustibility of timber is one of the main reasons to have the strict restriction on timber for use as a building material, especially for multistory buildings. Therefore, the main prerequisite for the use of timber in buildings is to ensure adequate fire resistance, using passive and active fire protection measures. This article contains the results of mechanical and fire experimental tests of both normal and innovative hollow glued laminated timber beams. A total of 10 timber beams were tested at ambient temperature, and 3 timber beams in fire conditions, which differed in cross-section type but also in the applied fire protection. The first beam was a normal GL beam without fire protection, the second a hollow beam covered by intumescent paint, while the third was also hollow, additionally protected by mineral wool infill inside the holes. The load-carrying capacity of the hollow beam in ambient conditions was estimated at 65% of the load-carrying capacity of a normal GL beam. Fire tests indicated that hollow timber beams with both intumescent paint and mineral wool infill failed at a similar time as a normal GL beam without fire protection. One-dimensional β0 and notional charring rates βn were obtained. Time to the protective material failure was 17 min. The main cause of failure of hollow beams was the appearance of delamination due to the reduction of the lamella bonding surface.

The basic concept of seismic building design is to ensure the ductility and sufficient energy dissipation of the entire system. The combination of wood and bearing glass represents a design in which each material transmits the load, and with the mutual and simultaneous interaction of the constituent elements, it is also earthquake resistant. Such a system has been developed so that the glass directly relies on the wooden frame, which allows the load to be transferred by contact and the friction force between the two of materials. Within the seismic load, friction between glass and wood is an important factor that affects both the behavior and performance of a wood–glass composite system. The set-up system consists of a single specimen of laminated or insulating glass embedded between two CLT elements. The friction force was determined at the CLT–glass contact surface for a certain lateral pressure, i.e., normal force. Friction depends on the way the elements (especially glass) are processed, as well as on the lateral load introduced into the system. Conducted experimental research was accompanied by numerical analyses. Experimental research was confirmed by numerical simulations.

Timber is one of the fundamental materials of human civilization, it is very useful and ecologically acceptable in its natural environment, and it fits very well with modern trends in green construction. The paper presents innovative hollow glued laminated (GL) timber elements intended for log-house construction. Due to the lack of data on the behavior of the hollow timber section in compression perpendicular to the grain, the paper presented involves testing the compression strength of elliptical hollow cross-section glue-laminated timber specimens made of softwood and hardwood, as well as full cross-section glue-laminated softwood timber specimens. The experimental research was carried out on a total of 120 specimens. With the maximal reduction of 26% compared to the full cross-section, regardless of the type of wood and direction of load, the compression strength perpendicular to the grain of hollow specimens decreases by about 55% compared to the full cross-section, with the coefficient kc,90 equal to 1.0. For load actions at the edge and the middle of the element, kc,90 factors were obtained with a value closer to those obtained for full cross-section, which indicates the same phenomenology, regardless of cross-sectional weakening. At the same time, the factors in the stronger axis are lower by about 10%, and in the weaker axis by about 30% compared to those prescribed by the Eurocode. Experimental research was confirmed by FEM analysis. Comparative finite element analysis was performed in order to provide recommendations for future research and, consequently, to determine the optimal cross-section form of the hollow GL timber element. By removing the holes in the central part of the cross-section, the stress is reduced. The distance of the holes from the edges defines the local cracking. Finally, if the holes are present only in the central part of the element, the behavior of the element is more favorable.

In the framework of the Cost Action CERTBOND (Reliable roadmap for certification of bonded primary structures), a wide group of researchers from 27 European Countries have had the opportunity to work on the topic of certification of bonded joints for primary structural applications from different engineering sectors such as the aerospace, automotive, civil engineering, wind energy and marine sectors. Since virtual testing and optimization are basic tools in the certification process, one of the key objectives of CERTBOND is to critically review some of the available models and failure theories for adhesive joints. The present paper summarizes the outcome of this task. Nine different models/theories are described in detail. Specifically, reviewed are the Classical Analytical Methods, the Process Zone Methods, Linear Elastic Fracture Mechanics (LEFM), the Virtual Crack Closure Technique (VCCT), the Stress Singularity Approach, Finite Fracture Mechanics (FFM), the Cohesive Zone Method (CZM), the Progressive Damage Modeling method and the Probabilistic methods. Also, at the end of the paper, the modeling of temperature effects on adhesive joints have been addressed. For each model/theory, information on the methodology, the required input, the main results, the advantages and disadvantages and the applications are given. Comisión Europea (Cooperación Europea en Ciencia y Tecnología) CA18120- CERTBOND

Due to the growing need to preserve our planet and reduce carbon emissions during construction, the use of the only carbon-absorbing material, timber, is increasingly being imposed. In addition to the requirement of reducing emissions, there is a necessity for the shortest possible construction time and the minimum use of construction machinery, which has led to the development of prefabricated construction systems. This paper deals with the innovative, hollow, glue-laminated timber elements which are intended for modular construction. Comparing this new system with existing modular systems, the main features and behavior of the constitutive elements, i.e., the hollow, glue-laminated timber elements, are presented. Experimental and numerical analysis of the mechanical performance of the timber elements was carried out and a comparative analysis of the behavior of two different types of hollow timber elements was conducted. The finite element method was used to predict the behavior of this innovative structural system. The results are compared with the analytical procedure to provide a background for the development of standardized methods for the design of timber structures.

The global objective of sustainable development has been greatly directed toward the preservation of existing structures. Therefore, condition assessment and reconstruction of existing timber structures have been gaining importance in recent times. This is particularly evident on timber roofs whose elements are exposed to degradation, either because of rheological effects or due to the direct influence of moisture and biological factors. In case of accidental events, such as an earthquake, the question of the structure’s condition is essential for the condition of the entire building. In order to prove the load-bearing capacity and serviceability of existing structures, as well as to check the need for reconstruction, it is necessary to define crucial parameters that are influencing the condition of materials, elements, and systems. Although there are many non destructive testing methods, the frequency and scope of their use, as well as the decision-making approach, have not been defined. In the paper, non-destructive and semi-destructive methods frequently used for timber structures are explained. A systematic review of criteria to be used in the assessment of load-bearing timber structures in a seismic active area was the main objective of this paper as well as the illustration of non-destructive and semi-destructive test methods through a case study involving roof construction of a hundred-year-old building in Zagreb, Croatia. Pre- and post-earthquake inspection was made. The overall condition of the roof structure after two significant earthquakes can be assessed as satisfactory given that the observed system is a large-span and massive roof structure. The presented results and identification of typical damages after the earthquake are presented in order to facilitate policy makers and for the future implementation of development strategies in the renovation of the city.

In seismic European countries, most of the residential building stock is earthquake-prone and highly energy-intensive because it was built before the enforcement of the recent seismic and energy codes. Furthermore, this stock often shows a low architectural quality due to poor maintenance and/or construction and design deficiencies. For all these reasons, it needs deep renovation. The use of common seismic and energy upgrading techniques however is often unsustainable in terms of costs, work duration, and occupants’ disturbance. Therefore, new integrated, affordable, fast, and low-disruptive renovation actions are strongly needed. This study proposes a seismic, energy-efficient renovation solution for masonry or reinforced concrete (RC) framed buildings, based on the addition of cross-laminated timber (CLT) panels to the outer walls, in combination with wooden framed hybrid panels made from the wooden frame and structural glass. Moreover, the CLT panels can be connected to the existing masonry structure or RC frame through innovative seismic energy dissipation devices. In case of an earthquake, these devices in combination with the CLT panels reduce the drift demand of the building, preventing, or reducing structural damages and consequent repair costs. Furthermore, strengthening of the old timber floor system is proposed also by CLT or LVL panels, coupled with existing floor timber beams, in a composite floor system that forms a stiff diaphragm. Another proposed solution is based on the complete demolition of the inner structure leaving only facades under the cultural protection and rebuilding the inner structure using CLT as a material of high strength, stiffness, and dimensional stability, good insulating performance, a renewable material with characteristics of quick installation (prefabricated systems built with high accuracy), cost-effectiveness, low disruption, reversibility, and low-carbon or zero carbon emission.

Bonded-in rods (BiR) represent a structural connection type that is largely used for new timber structures and rehabilitation (repair or reinforcement) of existing structural members. The technology is based on steel / Fiber Reinforced Polymer (FRP) / Glass Fiber Reinforced Polymer (GFRP) rods bonded into predrilled holes in timber elements. The mechanical advantages of BiRs include high local force capacity, improved strength, a relatively high stiffness and the possibility of ductile behaviour. They also offer aesthetic benefits, given that rods are hidden in the cross sections of wooden members. As such, BiR connections are regarded as a solution with great potential, but still uncertain design formulations. Several research projects have dealt with BiRs, but a final definition of their mechanics and a universal design procedure is still missing. This research study explores the typical fracture mechanics modes for BiR connections. A special focus is given to the evaluation of the impact of adhesive bonds under various operational conditions (i.e., moisture content of timber). A total of 84 specimens are tested in pull-out setup, and investigated with the support of digital image correlation (DIC). The reliability of empirical equations and a newly developed analytical model in support of design, based on linear elastic fracture mechanics (LEFM), is also assessed.

Cross laminated timber (CLT) beams are mainly used within wall panels, but also standalone in design situations where cross layers have a reinforcing effect concerning stress perpendicular to the beam axis. The stress state in CLT beam members is complex and shear failure is mainly governed by stresses and strains acting in the crossing areas between orthogonally bonded laminations, known as shear failure mode III. The current model suggested for the next version of Eurocode 5 regarding shear strength prediction has certain limitations. Based on model improvement, design proposals regarding shear failure mode III for CLT beams composed of 3 and 5 layers are expanded for CLT with 7 layers. Based on test results of small shear specimens, both design proposals successfully predict shear strength experimentally obtained on beam specimens. Evaluated full-field deformations by a digital image correlation (DIC) system and the improved model and design proposal coincide in regards to the critical crossing area position. The influence of reduced lamination widths on beam shear strength and shear strength ratio on the position of critical crossing areas are further analysed indicating a fairly minor contribution. The improved analytical model and design proposals were further modified to calculate the effective shear modulus of CLT beams. A good agreement between the analytical and test results is obtained for the slip modulus of the crossing areas proposed in the literature. However, a higher slip modulus seems appropriate for both design proposals in the design situation to avoid too conservative effective shear modulus and corresponding shear stiffness.

The work presented concerns validation of a specific analytical model for Cross Laminated Timber (CLT) at in-plane beam loading conditions. The original model (model A) has previously been presented in the literature and is also suggested to be used as a basis for design equations for the next version of Eurocode 5. An improved version (model B) of that original model (model A), regarding basic assumptions relating to the internal force distribution, has recently been presented in the literature. Here, comparisons between the original model (model A), the improved model (model B) and FE-analyses regarding magnitude and distribution of internal forces are presented. The main focus is on forces and torsional moments acting in the crossing areas between longitudinal and transversal laminations and relevant for shear mode III failure, meaning the relative sliding and rotation between two flat-side bonded laminations. The results show that the improved analytical model (model B) outperforms the original model (model A) in terms of giving predictions very close to the predictions of the FE-model. A further extension of the improved model (model B) regarding distribution of forces and torsional moments in the beam width direction is also presented.

Facade elements are known to represent a building component with multiple performance parameters to satisfy. Among others, “advanced facades” take advantage of hybrid solutions, like the assemblage of laminated materials. In addition to enhanced mechanical properties that are typical of optimally composed hybrid structural components, these systems are energy-efficient, durable, and offer lightening comfort and optimal thermal performance. This is the case of the structural solution developed in joint research efforts of the University of Zagreb and the University of Ljubljana, within the Croatian Science Foundation VETROLIGNUM project. The design concept involves the mechanical interaction of timber and glass load-bearing members, without sealing or bonded glass-to-timber surfaces. Laminated glass infilled timber frames are recognized as a new generation of structural members with relevant load-carrying capacity (and especially the enhancement of earthquake resistance of framed systems), but also energy-efficient and cost-effective solutions.

Cross laminated timber is an innovative plate-shaped product presenting a laminated structure and excellent physicomechanical properties. Due to its high stiffness and in-plane and out-of-plane bearing capacity, it is most often used in form of wall or floor panels. Favourable environmental, aesthetic and energy properties further enhance its qualities. The paper is a summary of CLT research conducted so far, with an emphasis on the need to harmonise existing regulations and include this product in the European standard for timber structures Eurocode 5.

Climate change is expected to have a severe impact on cultural heritage in the future. This study presents the methodology developed during the FP7 project Climate for Culture, of assessing the climate change impact on collection objects in cultural heritage buildings. The main innovation lies in coupling new high resolution future climate projections with building simulation tools in order to predict future indoor climate and identify future risks in historic buildings. The case study is an intermittently heated wooden chapel in Croatia. The whole building simulation model of the chapel was validated using a newly developed method of accuracy assessment in the context of preventive conservation. Even though modeling intermittent heating induces limitations in the model, it can be used for computing of future indoor data. Future indoor climate data was assessed for possible risks of biological, mechanical, and chemical damage to painted wooden panels using the newly developed specific climate risk assessment. When using this method of damage assessment on buildings with active climate control, especially with intermittent heating, it is recommended to determine the relevant season for the damage process in order to objectively analyze results.

Ocjena stanja i kontinuirano praćenje ponašanja postojećih drvenih konstrukcija u posljednje vrijeme sve više dobivaju na značaju. Globalni cilj održivog razvoja u velikoj mjeri usmjeren je na očuvanje postojećih konstrukcija i zaštitu graditeljske baštine. U radu su prikazane metode ocjenjivanja stanja postojećih drvenih konstrukcija. Glavni naglasak stavljen je na prikaz nedestruktivnih i poludestruktivnih metoda za drvene konstrukcije koje su često u uporabi. U radu su navedene metode na konkretnom primjeru ocjene stanja Tehničkog muzeja Nikole Tesle u Zagrebu., Condition assessment and continuous monitoring of the existing timber structures have been gaining in importance in recent times. The global objective of sustainable development has been greatly directed toward preservation of the existing structures and protection of architectural heritage. Methods used for assessing condition of the existing timber structures are presented in the paper. The main emphasis is placed on the presentation of non-destructive and semi-destructive methods for frequently used timber structures. The methods are presented through the example of condition assessment of the Nikola Tesla Technical Museum in Zagreb.

Cross laminated timber (CLT) is a versatile engineered timber product that is increasingly well-known and of global interest in several applications such as full size plane or linear timber elements. The aim of this study involves investigating the performance of CLT beams loaded in-plane by considering bending and shear stress analysis with a special emphasis on the in-plane shear behavior including the complex internal structure of CLT. Numerical analysis based on 3D-FE models was used and compared with two existing analytical approaches, namely representative volume sub element (method I) and composite beam theory (method II). The separate verification of bending and shear stresses including tree different shear failure modes was performed, and a good agreement was obtained. The main difference between the results relates to shear failure mode in the crossing areas between the orthogonally bonded lamellas in which the distribution of shear stresses τzx over the crossing areas per height of the CLT beam is not in accordance with the analytical assumptions. The presented analyses constitute the first attempt to contribute to the on-going review process of Eurocode 5 with respect to CLT beams loaded-in plane. Currently, regulations on designing these types of beams do not exist, and thus experimental and numerical investigations are planned in the future., Križno lamelirano drvo (CLT) svestrani je inženjerski proizvod na bazi drveta koji je sve poznatiji i globalne važnosti u različitim primjenama poput pločastih i linijskih elemenata velikih dimenzija. Prikazani rad usmjeren je na istraživanje ponašanja CLT greda opterećenih u ravnini elementa, uzimajući u obzir analizu naprezanja od savijanja i posmika, s naglaskom na posmična naprezanja u ravnini elementa i složenu unutrašnju strukturu CLT-a. Numerička analiza bazirana na 3D-FE modelima uspoređena je s dvama postojećim analitičkim pristupima pod nazivom reprezentativni volumni pod element (metoda I) i kompozitna štapna teorija (metoda II). Provedena je odvojena verifikacija naprezanja od savijanja i posmika uzimajući u obzir tri različita posmična mehanizma sloma, pri čemu je dobiveno dobro slaganje rezultata. Glavna razlika među rezultatima vezana je za posmični mehanizam sloma na kontaktu ortogonalno lijepljenih lamela, gdje se raspodjela posmičnih naprezanja τxz po lijepljenom kontaktu po visini CLT grede ne poklapa s teoretskim pretpostavkama. Prikazana analiza početni je doprinos trenutačno revidiranog Eurokoda 5, vezano za CLT grede opterećene u ravnini elementa. Trenutačno ne postoje propisi za njihovo dimenzioniranje pa su stoga daljnja eksperimentalna i numerička istraživanja ove tematike u planu.

Cross laminated timber (CLT), as a versatile engineered timber product, has in recent years become well-known and of global interests. The orthogonal laminar structure allows for application as beams, walls or panels for both out-of-plane and in-plane loading conditions. The work presented here concerns experimental investigations of in-plane loaded CLT beams, as very relevant from a practical engineering point of view due to reinforcing effect of transversal layers with respect to stress perpendicular to the beam axis. Experimental results are used for comparison and validation of design proposals from the literature, with the main focus on the shear failure mode III in crossing areas between orthogonally bonded longitudinal and transversal lamination. By using the assumed shear strength values from the literature, analytically predicted shear carrying capacities show good agreement with the experimentally obtained. Although further experimental validation is needed, obtained results indicate that suggested design proposals should be considered in ongoing revision work of Eurocode 5.

Fa&ccedil, ade elements are a building component that satisfies multiple performance parameters. Among other things, &ldquo, advanced fa&ccedil, ades&rdquo, take advantage of hybrid solutions, such as assembling laminated materials. In addition to the enhanced mechanical properties that are typical of optimally composed hybrid structural components, these systems are energy-efficient, durable, and offer lighting comfort and optimal thermal performance, an example of which is the structural solution developed in collaboration with the University of Zagreb and the University of Ljubljana within the Croatian Science Foundation VETROLIGNUM project. The design concept involves the mechanical interaction of timber and glass load-bearing members without sealing or bonding the glass-to-timber surfaces. Following earlier research efforts devoted to the structural analysis and optimization of thus-assembled hybrid Cross-Laminated Timber (CLT)-glass fa&ccedil, ade elements, in this paper, special focus is given to a thermal and energy performance investigation under ordinary operational conditions. A simplified numerical model representative of a full-size building is first presented by taking advantage of continuous ambient records from a Live-Lab mock-up facility in Zagreb. Afterwards, a more detailed Finite Element (FE) numerical analysis is carried out at the component level to further explore the potential of CLT&ndash, glass fa&ccedil, ade elements. The collected numerical results show that CLT&ndash, glass composite panels can offer stable and promising thermal performance for fa&ccedil, ades similar to national and European standard requirements.

Facade elements are known to represent a building component with multiple performance parameters to satisfy. Among others, “advanced facades” take advantage from hybrid solutions, like the assemblage of laminated materials. In addition to enhanced mechanical properties that are typical of optimally composed hybrid structural components, these systems are energy efficient, durable and offer lightening comfort and optimal thermal performance. This is the case of the structural solution developed in joint research efforts of University of Zagreb and University of Ljubljana, within the Croatian VETROLIGNUM project. The design concept involves the mechanical interaction of timber and glass load-bearing members, without sealing or glued glass-to-timber surfaces. Laminated glass infilled timber frames are in fact recognized as a new generation of structural members with relevant load-carrying capacity (and especially the enhancement of earthquake resistance of framed systems), but also energy-efficient and cost-effective solutions. In this paper, brief guidelines for the optimal structural design of glass infilled Cross-Laminated Timber (CLT) framed systems are presented. A special focus is then dedicated to the thermal performance assessment of these innovative CLT-glass facade modules under ordinary operational conditions. Finite Element numerical models of single elements are developed to reproduce a full-size mock-up building. The actual thermal performance is thus carried out with the support of continuous ambient records. The numerical results show that the CLT-glass composite facade system can be efficient and offer stable performances, in line with national and European standards requirements.

The TCC concept has been studied and developed over the past decades. The variety of solutions shows the meaningfulness and functionality of this system, as well as the continuous work of scientists over time. To benefit from these advantages, the composite needs to provide sufficient stiffness to meet the serviceability criteria and load capacity to resist loading at every stage of the building life. An example of connector types and load slip curves according to EN 1995 is given. This paper discusses possible limitations related to residential areas, and additionally, the possible solutions that EN 1995 does not discuss in the case of resonant response (f1 &lt, 8 Hz). The theoretical studies were accompanied by numerical analyses considering certain simplifications suitable for practical use.

Cross laminated timber (CLT) at in-plane beam loading conditions presents a complex stress state wherefore several failure modes and geometry parameters need to be considered in design. The work presented here includes experimental investigations of CLT beams for comparison and validation of an analytical model and design proposals previously suggested by the authors. All relevant failure modes are considered; bending failure and shear failure modes I, II and III. The main focus is, however, on shear failure mode III relating to shear failure in the crossing areas between orthogonally bonded longitudinal and transversal lamination. The analytical model presented is an improvement of the analytical model which has been suggested to be used as the basis for design equations for the next version of Eurocode 5. The two design proposals presented are based on that improved analytical model. Experimental results show good agreement with the improved model and both design proposals. In order to study the influence of different lamination placements and varying lamination widths, comparisons between the improved analytical model and FE-analyses regarding magnitude and distribution of internal forces are presented and good agreement is obtained. Experimental and analytical results indicate only a small influence of reduced lamination widths close to the beam edges. This is a finding which is of practical interest since CLT beams in general are cut from larger elements, with no consideration of the location of the individual laminations with respect to the edges of the beam.

Assessment and structural health monitoring of existing timber structures has experienced huge interest in last decades. The main reasons are clear messages that sustainable development is a long term goal of the global policy which results in modifications or substitutions or extensions of existing buildings and engineering works (Kyoto protocol 1997, all further World Climate Summits) beside protection and conservation of the heritage buildings built in timber and assessment and collection of crucial data for the design and long-term behavior of new structures in timber. At the moment, European norms (Eurocodes) cover engineering principles that could be used to form the basis of assessment of structures or structural elements but basically they are concepted for the design of new structures. In this paper assessment methods for timber structures are summarized and the most common ones are briefly explained. The main focus of the paper is to present non-destructive and semi-destructive test methods for timber structures and use of unmanned vehicle for gathering the data which were inputs for numerical model and structural analysis of the structure. The whole protocol is shown on actual case study of the H2020 Project INCEPTION, Technical Museum Nikola Tesla in Zagreb, Croatia.

Use of timber as a construction material has entered a period of renaissance since the development of high-performance engineered wood products, enabling larger and taller buildings to be built. In addition, due to substantial contribution of the building sector to global energy use, greenhouse gas emissions and waste production, sustainable solutions are needed, for which timber has shown a great potential as a sustainable, resilient and renewable building alternative, not only for single family homes but also for mid-rise and high-rise buildings. Both recent technological developments in timber engineering and exponentially increased use of engineered wood products and wood composites reflect in deficiency of current timber codes and standards. This paper presents an overview of some of the current challenges and emerging trends in the field of seismic design of timber buildings. Currently existing building codes and the development of new generation of European building codes are presented. Ongoing studies on a variety topics within seismic timber engineering are presented, including tall timber and hybrid buildings, composites with timber and seismic retrofitting with timber. Crucial challenges, key research needs and opportunities are addressed and critically discussed.

Innovative hybrid structural components composed of cross-laminated timber frame and laminated glass infill were tested to examine their response on the reverse-cyclic loading. Ductile timber-frame joints with glued-in steel rods and especially designed glass-to-timber contacts with no adhesive proved to provide high ductility and energy dissipation of structural components. In total, 20 tests of full-scale specimens were carried out; three bare frames, six frames with single glazing and eleven frames with double glazing. Deformation capacity, lateral strength, stiffness and strength deterioration and energy dissipation capacity were analysed in order to provide data for the future development of computational models and design guidance for the new codes.

Prilikom projektiranja konstrukcija u potresnim podrucjima, cesto se zahtijeva rjesenje kojim se postiže povecanje krutosti i nosivosti na seizmi

Cross laminated timber (CLT), being a versatile engineered timber product, has in recent years become well-known and of global interest. The orthogonal, laminar structure allows for application as full size elements for both out- of- plane and in-plane loading conditions. The work to be presented concerns in-plane loaded CLT beams, whose use is very relevant from a practical engineering point of view since the transversal layers have a reinforcing effect with respect to stress perpendicular to the beam axis. Due to the layered composition of CLT, the stress state is complex and several failure modes and geometry parameters need to be considered in design. In addition to the basic material strength parameters and gross cross section dimensions, the beam strength is furthermore affected by the ratio of the longitudinal and transversal layer widths and by the dimensions of the cross sections of the individual laminations. Several experimental tests on CLT beams have been conducted, e.g. by Bejtka (2011), Flaig (2013) and Danielsson et al (2017a, 2017b). An analytical composite beam model for stress analysis and strength verification has been presented by Flaig & Blass (2013), including stress based failure criteria for relevant failure modes. That model includes two basic assumptions related to the shear stresses acting in the crossing areas between the longitudinal and transversal laminations and relevant for shear failure mode III: 1) the stresses are, irrespective of the element lay-up, uniformly distributed in the beam width direction and 2) the torsional moments/stresses are uniformly distributed over all crossing areas in the beam height direction. Based on comparison to 3D FE- analyses as presented by Jelec et al (2016) and Danielsson et al (2017a), both these assumptions seem to be inaccurate. The aim of the paper is to present improvements of the model by Flaig & Blass (2013), regarding stress analysis and strength verification with respect to shear mode III failure of prismatic CLT beams. The improvements concern the magnitude and the distribution of the internal forces and torsional moments acting in the crossing areas between longitudinal and transversal laminations. Of specific interest is the non-uniform distributions in the beam width and height directions. The improved analytical model will be presented in exact and simplified forms and compared to the model as presented by Flaig & Blass. Internal force distributions according to the analytical models will also be compared to results of full 3D FE- analysis.

Križno lamelirano drvo (eng. Cross Laminated Timber – CLT) inovativni je pločasti proizvod slojevite strukture i izvrsnih fizikalno-mehaničkih svojstava. Zbog velike krutosti i nosivosti u ravnini i okomito na ravninu elementa najčešće se primjenjuje u obliku zidnih ili stropnih panela. Povoljna ekološka, estetska i energetska svojstva dodatno ga pospješuju. Rad prikazuje sumarni pregled dosad provedenih istraživanja CLT-a, s naglaskom na potrebnu harmonizaciju postojećih propisa i njegovo uključivanje u europsku normu za drvene konstrukcije Eurokod 5., Cross laminated timber is an innovative plate-shaped product presenting a laminated structure and excellent physicomechanical properties. Due to its high stiffness and in-plane and out-of-plane bearing capacity, it is most often used in form of wall or floor panels. Favourable environmental, aesthetic and energy properties further enhance its qualities. The paper is a summary of CLT research conducted so far, with an emphasis on the need to harmonise existing regulations and include this product in the European standard for timber structures Eurocode 5., Brettsperrholz (eng. ross Laminated Timber – CLT) ist ein innovatives plattenförmiges Produkt mit einer geschichteten Struktur und hervorragenden physikalischmechanischen Eigenschaften. Aufgrund der hohen Steifigkeit und Tragfähigkeit in Ebene und senkrecht zur Ebene des Elements wird es meistens in Form von Wand- oder Deckenpaneelen verwendet. Die günstigen ökologischen, ästhetischen und energiewirtschaftlichen Eigenschaften verbessern dieses noch zusätzlich. Die Abhandlung gibt eine zusammenfassende Übersicht über die bisherigen Untersuchungen des CLT mit Betonung auf der erforderlichen Harmonisierung der bestehenden Vorschriften und dessen Integration in die europäische Norm Eurocode 5 für Holzkonstruktionen.

The conservation of historical timber structures requires both the knowledge of structural behavior of complete building and behavior of any single element in the structure. Due to poor communication between the institutions dealing with conservation and restoration of buildings and institutions that urgently require structure renovation, renovation of historic buildings is often performed inappropriately with respect to engineering and architectural approach. Buildings are frequently subjected to inappropriate interventions, replacements of structural elements, or even worse, they are demolished. First case study in this paper is Cathedral from Gospić, which was subjected to inappropriate reconstruction in the 1990s. The cathedral was demolished during the war and the tower and roof structure were subjected to reconstruction. The second case study is a small traditionally constructed timber chapel in the village Lijevi Štefanki, which represents a valuable monument of rural cultural heritage. Visual inspection of the chapel was done and recommendations for reconstruction were proposed.

Technical Museum is one of the most visited Museums in Zagreb (capital of Croatia). The museum presents scientific and educational centre in the field of technical sciences. The entire structure of the Museum is constructed as a timber structure and as such represents a rare existing example of the European engineering concept of expo-halls timber structures with large span (85m x 40 m) from the early 20 century. In this article overview of different NDTs that were performed in order to assess the structural performance of elements is given; moisture ratio and ultrasound investigations are carried out in situ in order to investigate timber condition. Based on the detected state of the structure reconstruction measures are presented.

Cultural heritage assets, the bearers of historic evidence, are under continuous pressure from change, deterioration, and destruction. Therefore, there is a need to identify and monitor the related risks and to develop appropriate measures for increasing the resilience of cultural heritage. The activities for establishing a European system for data collection and its application in the field of preventive conservation are an ongoing process, where the issue of risks and resilience is well addressed. Recently, there has been an interest in developing a model of built heritage resilience related to mitigation and reaction on sudden environmental impacts, following the resilience models of contemporary buildings. However, these models cannot be simply extended to heritage buildings because of their specific character. In this chapter, a contribution to an acceptable resilience model of heritage buildings is presented.